Unlike automobiles that have horizontally-oriented exhaust pipes, large trucks with diesel engines typically have vertically-oriented exhaust pipes known as exhaust stacks. A diesel exhaust stack is vertically-oriented so that heavy, noxious and smoky diesel engine fumes (and combustion products) are exhausted at an elevation above surrounding traffic to minimize annoyance to other drivers. As a result of the stack's vertical orientation, the opening or exhaust outlet at the top of the exhaust stack is generally exposed and more likely to have rain, leaves, bird droppings or other unwanted matter inadvertently fall into the outlet of the stack. This problem is amplified when the diesel engine is not running. When the diesel engine is running, any debris is hopefully repelled or dispelled by the exhaust flow. Without exhaust flow, nothing prevents the debris from falling into the exhaust stack.
To combat the tendency for debris to easily fall into a vertical exhaust stack, many diesel engine exhaust stacks are designed to terminate in a bend. This bend changes the orientation of the exhaust outlet from a horizontal to a vertical plane. However, a curved exhaust stack may still become plugged by debris or rain, particularly when the truck is not moving and the wind drives rain and debris at an angle to vertical.
Other methods have been used to address the problem of unwanted debris falling into a vertical diesel exhaust stack. One prior art product, commonly known as a clapper, includes a hinged, spring-loaded lid that covers the top of an exhaust stack whenever the diesel engine is not operating. The hinge spring tension is adjusted to allow the clapper lid to open whenever exhaust pressure is present i.e., the diesel engine is running. Unfortunately, clapper covers are not fail-safe. If the spring tension is too low, the clapper may fail in an open position, providing no protection whatsoever. Additionally, if the spring tension is excessive, the clapper may not open sufficiently when the diesel engine is running. As a result, increased back pressure is placed on the diesel engine combustion chamber, negatively affecting engine performance and creating difficulties when attempting to start the engine.
A further limitation of the clapper type cover is its fixed spring constant in its hinge spring. Given a fixed spring constant, the clapper type cover will open and close as the exhaust pressure at the outlet of exhaust stack varies. This open and closing action is particularly noticeable when the engine is at idle or low RPM. During this state, the exhaust pulse is more noticeable, creating a cyclic rather than continuous exhaust flow and outlet pressure. The opening and closing action can create substantial noise as the clapper cyclically slams shut on the top of the exhaust pipe. The resulting clapping noise is extremely annoying to the truck operator.
Accordingly, a need exists for a simple and expedient means to cover the exhaust outlet of a vertically-oriented exhaust pipe or stack to prevent inadvertent entry of unwanted debris or fluids when the truck is at rest.